An
ornament for a courtyard at a World's Fair is to be made up of four identical,
frictionless metal spheres, each weighing 2√6
ton-wts . The spheres are to be arranged
as shown, with three resting on a horizontal surface and touching each other;
the fourth is to rest freely on the other three. The bottom three are kept from
separating by spot welds at the points of contact with each other. Allowing for
a factor of 3, how much tension must the spot welds withstand?

Answer:
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